Power supply apparatus, motor drive control method using the same and motor vehicle having the same mounted thereon

ABSTRACT

A power supply apparatus driving and controlling motor generators (MG 1 , MG 2 ) includes a battery ( 10 ) generating an input voltage (Vb), a converter ( 110 ) converting the input voltage into a motor operating voltage (Vm) according to a voltage command value (Vmr), a smoothing capacitor ( 120 ) holding the motor operating voltage, inverters ( 131, 132 ) receiving the motor operating voltage and driving and controlling the motor generators (MG 1 , MG 2 ) according to a torque command value (Tref), and a control unit ( 15 ) generating the voltage command value and the torque command value. When the motor generators (MG 1 , MG 2 ) operate in the power running mode, the control unit ( 15 ) operates to make the torque command value smaller than an original required torque as necessary so as to allow the sum of electric power (Pm) consumed by the motors and an amount of change (Pc) in stored electric power of the smoothing capacitor ( 120 ) caused as the motor operating voltage increases not to exceed an output electric power limiting value (Pcvlm) of the converter ( 110 ).

TECHNICAL FIELD

The present invention relates to a power supply apparatus and a motordrive control method. In particular, the present invention relates to apower supply apparatus driving and controlling a motor by converting thelevel of an input DC (direct current) voltage, a method of driving andcontrolling a motor using the power supply apparatus, and a motorvehicle having the power supply apparatus mounted thereon.

BACKGROUND ART

Hybrid electric vehicles and electric vehicles including, in a driveapparatus thereof, an electric motor which transforms electrical energyinto mechanical energy have recently been of great interest asenvironment-friendly vehicles. The hybrid electric vehicles are nowpartially commercialized. Some types of hybrid electric vehicles employa structure having a power supply apparatus driving and controlling amotor, the apparatus being provided with the ability of converting thelevel of a DC voltage input thereto for allowing a voltage applied fordriving the motor (hereinafter referred to as “motor operating voltage”)to be adjustable according to operating conditions (e.g. number ofrevolutions, torque) of the motor, in order to highly efficiently drivethe motor. In particular, the power supply apparatus is provided with avoltage step-up ability to make the motor operating voltage higher thanthe input DC voltage. Thus, a battery serving as a DC voltage source isreduced in size and the increased voltage allows the power loss toreduce, making it possible to improve efficiency of the motor.

For example, Japanese Patent Laying-Open No. 2003-244801 discloses astructure of driving and controlling an AC (alternating current)electric motor for driving wheels. In this structure, a DC voltage froma battery comprised of secondary cells is increased by means of avoltage step-up converter to generate a motor operating voltage, and themotor operating voltage is converted into an AC voltage by means of aninverter. With this structure, the voltage step-up ratio of the voltagestep-up converter is set according to conditions of the motor and thusthe motor can be operated highly efficiently.

For the aforementioned structure, however, a smoothing capacitor forstabilizing the motor operating voltage has to be provided on the outputside of the converter which converts the level of the input voltage, astaught in Japanese Patent Laying-Open No. 2003-244801. Thus, when themotor operating voltage is changed according to operating conditions ofthe motor, the voltage held by the smoothing capacitor changes to causestored electric power (P=C·V²/2) thereof to change.

Accordingly, when the motor operates under power running mode to convertelectrical energy supplied thereto into mechanical energy (hereinafterreferred to as “power running mode”) and an instruction to increase themotor operating voltage is issued according to increase in number ofrevolutions and torque of the motor, the stored electric power of thesmoothing capacitor is accordingly increased. In the process of theincrease in stored electric power of the smoothing capacitor, theconverter supplies not only electric power to be consumed by the motorbut also the electric power corresponding to the increase in storedelectric power of the smoothing capacitor. Consequently, a situationwhere the converter outputs excessive electric power could be caused.

In particular, when the battery serving as the input voltage source hasits power supply ability higher than the capacity of a switching devicethat constitutes the converter and thus the output electric power of theconverter is limited by the capacity (electric current capacity) of theswitching device, the switching device could be broken under theaforementioned situation, resulting in a failure in hardware.

On the contrary, when the motor operates under regenerative brakingcontrol to convert mechanical braking energy into electrical energy(hereinafter referred to as “regenerative mode”) and thereby supply theregenerative electric power from the motor to the battery and the motoroperating voltage is decreased according to decreases in number ofrevolutions and torque of the motor, the regenerative electric powerfrom the motor as well as electric power corresponding to the decreasein stored electric power of the smoothing capacitor are provided to theconverter. Consequently, electric current passing through the switchingdevice constituting the converter increases and the aforementionedsituation could also be caused.

DISCLOSURE OF THE INVENTION

The present invention has been made for solving the above-describedproblems. An object of the present invention is to provide a powersupply apparatus driving and controlling a motor by converting the levelof an input DC voltage, the power supply apparatus being structured tobe able to perform control in such a manner that prevents excessiveelectric current from flowing through a converter which is provided forconverting the level, and to provide a motor vehicle having the powersupply apparatus as described above.

A power supply apparatus according to the present invention is a powersupply apparatus driving and controlling a motor and includes a DC powersupply, a converter, an electric charge storage unit, a motor drivecontrol unit, and a control unit. The converter converts a first DCvoltage from the DC power supply into a second DC voltage according to avoltage command value to output the second DC voltage between a firstpower supply line and a second power supply line. The electric chargestorage unit is chargeable and dischargeable and connected between thefirst power supply line and the second power supply line. The motordrive control unit receives the second DC voltage between the firstpower supply line and the second power supply line and converts,according to a driving force command value, the second DC voltage intoelectric power for driving and controlling the motor. The control unitadjusts, when the motor operates in a power running mode to convertelectrical energy into mechanical energy, the driving force commandvalue to allow the sum of electric power consumed by the motor accordingto the driving force command value and an amount of change in storedelectric power of the electric charge storage unit, the change beingcaused as the second DC voltage changes, to be smaller than a limitingvalue of electric power output from the converter.

Preferably, the voltage command value is determined according to thenumber of revolutions and a required driving force of the motor andindependently of the driving force command value.

Still preferably, the DC power supply is chargeable, the motor drivecontrol unit converts, when the motor operates in a regenerative mode togenerate regenerative electric power from mechanical energy, theelectric power generated by the motor into the second DC voltageaccording to the voltage command value and outputs the second DC voltagebetween the first power supply line and the second power supply line,the converter converts, when the motor operates in the regenerativemode, the second DC voltage into the first DC voltage to charge the DCpower supply, and the control unit adjusts, when the motor operates inthe regenerative mode, the voltage command value as required based on arelation between a combination of the electric power generated by themotor and an amount of change in stored electric power of the electriccharge storage unit that is caused by a change of the second DC voltageand a limiting value of electric power input to the converter.

Still preferably, when the motor operates in the regenerative mode, thevoltage command value is adjusted by the control unit as required, aftertemporarily determined according to the number of revolutions and arequired driving force of the motor.

Still preferably, the control unit inhibits, when the motor operates inthe regenerative mode and the electric power generated by the motorexceeds the limiting value of electric power input to the converter,decrease of the voltage command value.

Still preferably, the control unit restricts, when the motor operates inthe regenerative mode and the electric power generated by the motor issmaller than the limiting value of electric power input to theconverter, an amount of decrease in the voltage command value so as tobalance the amount of change in stored electric power of the electriccharge storage unit that is caused by the change of the second DCvoltage with a combination of the limiting value of electric power inputto the converter and the electric power generated by the motor.

A motor vehicle according to the present invention includes a powersupply apparatus as recited in any of claims 1 to 6, and an AC electricmotor provided as the motor driven and controlled by the power supplyapparatus and capable of driving at least one wheel. The converter isprovided as a voltage step-up converter capable of making the second DCvoltage higher than the first DC voltage. The motor drive control unitincludes an inverter making conversion between the second DC voltage andan AC voltage for driving and controlling the AC electric motor.

A motor drive and control method according to the present invention is amotor drive and control method for driving and controlling a motor by apower supply apparatus, the power supply apparatus including: a DC powersupply; a converter converting a first DC voltage from the DC powersupply into a second DC voltage according to a voltage command value tooutput the second DC voltage between a first power supply line and asecond power supply line; a chargeable and dischargeable electric chargestorage unit connected between the first power supply line and thesecond power supply line; and a motor drive control unit converting,according to a driving force command value, the second DC voltagebetween the first power supply line and the second power supply lineinto electric power for driving and controlling the motor, and includesa first step of adjusting, when the motor operates in a power runningmode to convert electrical energy into mechanical energy, the drivingforce command value to allow the sum of electric power consumed by themotor according to the driving force command value and an amount ofchange in stored electric power of the electric charge storage unit, thechange being caused as the second DC voltage changes, to be smaller thana limiting value of electric power output from the converter.

Preferably, according to the motor drive and control method of thepresent invention, the voltage command value is determined according tothe number of revolutions and a required driving force of the motor andindependently of the driving force command value.

Still preferably, the motor drive and control method of the presentinvention further includes a second step. The DC power supply ischargeable, the motor drive control unit converts, when the motoroperates in a regenerative mode to generate regenerative electric powerfrom mechanical energy, the electric power generated by the motor intothe second DC voltage according to the voltage command value and outputsthe second DC voltage between the first power supply line and the secondpower supply line, the converter converts, when the motor operates inthe regenerative mode, the second DC voltage into the first DC voltageto charge the DC power supply. The second step adjusts, when the motoroperates in the regenerative mode, the voltage command value as requiredbased on a relation between a combination of the electric powergenerated by the motor and an amount of change in stored electric powerof the electric charge storage unit that is caused by a change of thesecond DC voltage and a limiting value of electric power input to theconverter.

Still preferably, according to the motor drive and control method of thepresent invention, when the motor operates in the regenerative mode, thevoltage command value is temporarily determined, before the second stepis carried out, according to the number of revolutions and a requireddriving force of the motor.

Still preferably, according to the motor drive and control method of thepresent invention, the second step includes a sub step of inhibiting,when the motor operates in the regenerative mode and the electric powergenerated by the motor exceeds the limiting value of electric powerinput to the converter, decrease of the voltage command value.

Still preferably, according to the motor drive and control method of thepresent invention, the second step includes a sub step of restricting,when the motor operates in the regenerative mode and the electric powergenerated by the motor is smaller than the limiting value of electricpower input to the converter, an amount of decrease in the voltagecommand value so as to balance the amount of change in stored electricpower of the electric charge storage unit that is caused by the changeof the second DC voltage with a combination of the limiting value ofelectric power input to the converter and the electric power generatedby the motor.

Preferably, regarding the power supply apparatus and the motor drive andcontrol method of the present invention, the amount of change in storedelectric power is calculated based on the voltage command value.Preferably, in the first or second step, the amount of change in storedelectric power is calculated based on a detected value of the second DCvoltage.

With the power supply apparatus and the motor drive and control methodaccording to the present invention, when the motor operates in the powerrunning mode, the driving force command value is adjusted to reduceelectric power consumed by the motor as required, so that electric poweroutput from the converter does not become excessive, in consideration ofa change in stored electric power of the electric charge storage unitthat is caused as the second DC voltage (motor operating voltage)changes according to the voltage command value.

Accordingly, with the structure having the converter capable of varyingthe voltage (motor operating voltage) supplied to the motor drivecontrol unit (inverter), overcurrent of the converter can be preventedto provide device protection. In particular, the voltage command valueof the second DC voltage (motor operating voltage) is determinedaccording to the number of revolutions and a required torque of themotor and thus efficiency of the motor can be improved.

Further, when the motor operates in the regenerative mode, the voltagecommand value is adjusted as required to restrict decrease of the secondDC voltage (motor operating voltage) in consideration of a change instored electric power of the electric charge storage unit, so thatelectric power input to the converter does not become excessive.Overcurrent of the converter can thus be prevented to provide deviceprotection.

In particular, an amount of decrease of the voltage command value isrestricted based on a comparison between the electric power generated bythe motor and the limiting value of electric power input to theconverter. Thus, the motor can be improved in efficiency within therange in which the limiting value of electric power input to theconverter is not exceeded.

The motor vehicle according to the present invention is structured tohave the converter mounted thereon that serves as a voltage step-upconverter for varying a voltage input to the inverter (second DCvoltage) driving and controlling the AC electric motor which driveswheels, and thereby improve efficiency in operation of the AC electricmotor. When the AC electric motor operates in the electric motor mode,the driving force command value can be adjusted to reduce electric powerconsumed by the motor as required, so that electric power output fromthe converter does not become excessive, in consideration of a change instored electric power of the electric charge storage unit that is causedas the second DC voltage changes according to the voltage command value.Accordingly, overcurrent of the converter can be prevented to providedevice protection.

Further, when the AC electric motor operates in the regenerative mode,the regenerative electric power of the AC electric motor can be limitedto prevent overcurrent of the converter and thereby provide deviceprotection, without deterioration in braking ability.

Here, the change in stored electric power of the electric charge storageunit may be calculated based on the voltage command value so as toreduce a load of calculation for control.

Moreover, the change in stored electric power of the electric chargestorage unit may be calculated based on a detected value of the secondDC voltage so as to improve control accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a structure of a motor vehiclehaving a power supply apparatus according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of the powersupply apparatus according to the present invention.

FIG. 3 schematically illustrates a manner of calculation of an optimummotor voltage.

FIG. 4 is a circuit diagram showing a specific example of theconfiguration of a PCU shown in FIG. 2.

FIG. 5 is a flowchart illustrating electric power balance control in thepower running mode.

FIG. 6 is a flowchart illustrating electric power balance control in theregenerative mode.

BEST MODES FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is hereinafter described indetail with reference to the drawings. Here, like components in thedrawings are denoted by like reference characters and the descriptionthereof will not be repeated.

FIG. 1 is a block diagram illustrating a structure of a motor vehiclehaving a power supply apparatus according to the present invention.

Referring to FIG. 1, hybrid electric vehicle 100 of the presentinvention includes a battery 10, an ECU (Electronic Control Unit) 15, aPCU (Power Control Unit) 20, a motive power output apparatus(hereinafter referred to as “power output apparatus”) 30, a DG(Differential Gear) 40, front wheels 50L, 50R, rear wheels 60L, 60R,front seats 70L, 70R, and a rear seat 80.

Battery 10 is comprised for example of nickel-hydride or lithium-ionsecondary cells, supplies a DC voltage to PCU 20 and is charged with aDC voltage from PCU 20. Battery 10 is placed for example behind rearsheet 80 and electrically connected to PCU 20. PCU 20 generallyrepresents an electric-power converter that is necessary in hybridelectric vehicle 100.

To ECU 15, various sensor outputs 17 of various sensors that indicaterunning conditions and vehicle conditions are provided. Various sensoroutputs 17 include for example the pedal travel of an accelerator thatis detected by a position sensor placed on an accelerator pedal 35 andan output of a wheel-speed sensor. ECU 15 comprehensively performsvarious control operations for hybrid electric vehicle 100.

Power output apparatus 30 includes an engine and motor generators MG1,MG2 provided as sources of motive power for driving the wheels. DG 40transmits motive power from power output apparatus 30 to front wheels50L, 50R and transmits a rotational force of front wheels 50L, 50R topower output apparatus 30.

Accordingly, power output apparatus 30 transmits motive power generatedby the engine and/or motor generators MG1, MG2 via DG 40 to front wheels50L, 50R and thereby drives front wheels 50L, 50R. Further, power outputapparatus 30 generates electric power from a rotational force of motorgenerators MG1, MG2 that is originated in front wheels 50L, 50R andsupplies the generated electric power to PCU 20. In other words, motorgenerators MG1, MG2 serve as an “AC electric motor” capable of drivingat least one wheel.

When motor generators MG1, MG2 operate in the power running mode, PCU 20follows a control instruction from ECU 15 to step up the DC voltage frombattery 10 and convert the increased DC voltage into an AC voltage andthereby drive and control motor generators MG1, MG2 included in poweroutput apparatus 30.

Further, when motor generators MG1, MG2 operate in the regenerativemode, PCU 20 follows a control instruction from ECU 15 to convert an ACvoltage generated by motor generators MG1, MG2 into a DC voltage andthereby charge battery 10.

In hybrid electric vehicle 100 as discussed above, battery 10, PCU 20and a portion of ECU 15 that controls PCU 20 constitute a “power supplyapparatus” driving and controlling motor generators MG1, MG2.

A configuration of the power supply apparatus according to the presentinvention is now described.

Referring to FIG. 2, the power supply apparatus of the present inventionincludes battery 10 corresponding to “DC power source,” a portion of PCU20 that is involved in drive and control of motor generators MG1, MG2(this portion is also referred to as “PCU 20” hereinafter), and theportion of ECU 15 that is involved in control of PCU 20 (this portion isreferred to as “control unit 15” hereinafter).

PCU 20 includes a converter 110, a smoothing capacitor 120, motor drivecontrollers 131, 132 associated respectively with motor generators MG1,MG2, and a converter/inverter control unit 140. In this embodiment,motor generators MG1, MG2 that are AC motors are driven and controlled.Therefore, the motor drive controllers are constructed of inverters.Motor drive controllers 131, 132 are thus referred to as inverters 131,132 hereinafter.

Control unit 15 determines, based on various sensor outputs 17, arequired torque Trq of motor generators MG1, MG2 in consideration forexample of the distribution ratio of output power between the engine andthe motor generators (this ratio is also referred to as “output ratio”hereinafter). Further, control unit 15 calculates an optimum motoroperating voltage Vm# according to operating conditions of motorgenerators MG1, MG2.

As shown in FIG. 3, optimum operating voltage Vm# for improvingefficiency of motor generators MG1, MG2 is determined based on thenumber of motor revolutions (hereinafter referred to as motor revolutionnumber) N and required torque Trq. For the same required torque Trq,optimum motor operating voltage Vm# increases as motor revolution numberN increases. For the same motor revolution number N, optimum motoroperating voltage Vm# increases as required torque Trq increases.

Control unit 15 controls electric power balance, which is hereinlaterdescribed in detail, based on required torque Trq and optimum motoroperating voltage Vm# and generates a voltage command value Vmr of amotor operating voltage Vm and a torque command value Tref of motorgenerators MG1, MG2.

Voltage command value Vmr and torque command value Tref are provided toconverter/inverter control unit 140. To converter/inverter control unit140, control unit 15 further provides an identification signal SMTindicating whether motor generators MG1, MG2 operate in the powerrunning mode or the regenerative mode.

Following voltage command value Vmr from control unit 15,converter/inverter control unit 140 generates a converter control signalScnv for controlling operation of converter 110. Following torquecommand value Tref from control unit 15, converter/inverter control unit140 generates inverter control signals Spwm1, Spwm2 for controllingrespective operations of inverters 131, 132.

With reference to FIG. 4, a specific example of the configuration of PCU20 shown in FIG. 2 and operation thereof are described.

Referring to FIG. 4, the positive electrode and the negative electrodeof battery 10 are connected respectively to power supply lines 101, 102.

Converter 110 includes a reactor 115, switching elements Q1, Q2 anddiodes D1, D2,

Switching elements Q1, Q2 are connected in series between power supplylines 103, 102. Reactor 115 is connected between power supply line 101and a connection node Nm of switching elements Q1, Q2. Betweenrespective collectors and respective emitters of switching elements Q1,Q2, respective anti-parallel diodes D1, D2 are connected for allowingelectric current to flow from the emitter to the collector.

To respective gates of switching elements Q1, Q2, gate control signalsGS1, GS2 corresponding to converter control signal Scnv are provided. Inresponse to respective gate control signals GS1, GS2, turn-on/off ofswitching elements Q1, Q2 is controlled. As the switching elements ofthis embodiment, IGBT (Insulated Gate Bipolar Transistor) is employedfor example.

Smoothing capacitor 120 is connected between power supply lines 103,102.

Inverter 131 is a three-phase inverter comprised of switching elementsQ3 to Q8 constituting a U-phase arm 151, a V-phase arm 152 and a W-phasearm 153 connected in parallel between power supply lines 103, 102.Between respective collectors and respective emitters of switchingelements Q3 to Q8, anti-parallel diodes D3 to D8 are connectedrespectively.

To respective gates of switching elements Q3 to Q8, gate control signalsGS3 to GS8 corresponding to inverter control signal Spwm1 are provided.By a portion of a drive apparatus (not shown), switching elements Q3 toQ8 are turned on/off in response to gate control signals GS3 to GS8.

The intermediate point of each phase arm of inverter 131 is connected toone end of a corresponding phase coil of motor generator MG1 which is athree-phase permanent magnet motor generator. Respective other ends ofthe phase coils are commonly connected to the intermediate point.Further, at least two of the three phases are provided with currentsensors 161, 162 so that each phase current can be detected.

Inverter 132 is also a three-phase inverter similar to inverter 131 thatis comprised of switching elements Q3# to Q8# and anti-parallel diodesD3# to D8#. To respective gates of switching elements Q3# to Q8#, gatecontrol signals GS3# to GS8# corresponding to inverter control signalSpwm2 are provided. By a portion of the drive apparatus (not shown),switching elements Q3# to Q8# are turned on/off in response to gatecontrol signals GS3# to GS8#.

The intermediate point of each phase arm of inverter 132 is connected toone end of a corresponding phase coil of motor generator MG2. Respectiveother ends of the phase coils of motor generator MG2 are commonlyconnected to the intermediate point. To at least two of the threephases, current sensors 161#, 162# are provided so that each phasecurrent can be detected.

No limitation is imposed on the number of phases (three phases) and theform (permanent magnet motor) of motor generators MG1, MG2, and anyarbitrary AC electric motors are applicable.

Operation of the power supply apparatus when motor generators MG1, MG2operate in the power running mode is now described.

Battery 10 supplies an input voltage Vb corresponding to “first DCvoltage” between power supply lines 101, 102.

Converter 110 receives input voltage Vb between power supply lines 101,102 that is supplied from battery 10, steps up input voltage Vb throughswitching control of switching elements Q1, Q2 to generate motoroperating voltage Vm corresponding to “second DC voltage” and outputsthe generated voltage between power supply lines 103, 102. Power supplylines 103, 102 thus constitute “first power supply line” and “secondpower supply line” respectively. The voltage step-up ratio (Vm/Vb) atconverter 110 is determined by the ratio between respective ON periods(duty ratio) of switching elements Q1, Q2.

Accordingly, converter/inverter control unit 140 determines the voltagestep-up ratio at converter 110 based on voltage command value Vmr fromcontrol unit 15 and generates gate control signals GS1, GS2 so that thisstep-up ratio is satisfied.

Between power supply lines 103, 102, smoothing capacitor 120 that ischargeable and dischargeable and provided as “electric charge storageunit” smoothes motor operating voltage Vm provided from converter 110.

In response to gate control signals GS3 to GS8 and GS#3 to GS#8,inverters 131, 132 convert motor operating voltage Vm between powersupply lines 103, 102 into an AC voltage for driving motor generatorsMG1, MG2.

Converter/inverter control unit 140 generates, according to respectiveoutput values of various sensors, inverter control signals Spwm1, Spwm2to allow motor current to flow through each phase of motor generatorsMG1, MG2 so that a torque according to torque command value Tref and thenumber of revolutions according to a target number of revolutions aregenerated. For example, gate control signals GS3 to GS8 and GS3# to GS8#corresponding to inverter control signals Spwm1, Spwm2 are PWM signalwaves generated in accordance with a generally employed control scheme.

The output values of various sensors include for example respectiveoutput values of position sensors and speed sensors of motor generatorsMG1, MG2, respective output values of current sensors 161, 162, 161#,and 162# and an output of a voltage sensor detecting motor operatingvoltage Vm.

In contrast, when motor generators MG1, MG2 operate in the regenerativemode, operation of the power supply apparatus is controlled in thefollowing manner. Here, the regenerative mode of motor generators MG1,MG2 includes braking accompanied by regenerative power generation thatis effected when a driver of hybrid electric vehicle 100 steps on thefoot brake as well as deceleration (or acceleration) of the vehicleaccompanied by regenerative power generation that is effected when thedriver releases the accelerator pedal without operating the foot brake.

Converter/inverter control unit 140 detects from identification signalSMT from ECU 15 that hybrid electric vehicle 100 starts to operate inthe regenerative mode. In response thereto, converter/inverter controlunit 140 generates inverter control signals Spwm1, Spwm2 so that an ACvoltage generated by motor generators MG1, MG2 is converted by inverters131, 132 into a DC voltage.

Accordingly, inverters 131, 132 convert the AC voltage generated bymotor generators MG1, MG2 into a DC voltage (i.e., motor operatingvoltage Vm) in accordance with voltage command value Vmr and output thegenerated voltage between power supply lines 103, 102.

In the regenerative mode, converter/inverter control unit 140 generatesconverter control signal Scnv so that the DC voltage (motor operatingvoltage Vm) provided from inverters 131, 132 is stepped down. In otherwords, in the regenerative mode, switching elements Q1, Q2 of converter110 are turned on/off in response to respective gate control signalsGS1, GS2 so that motor operating voltage Vm is stepped down and DCvoltage Vb is output between power supply lines 101, 102. Battery 10 isthus charged with DC voltage Vb from converter 110. In this way,converter 110 can also step down motor operating voltage Vm to DCvoltage Vb and thus has the function of a bidirectional converter.

The basic operation of the power supply apparatus that is involved indrive and control of the motor generators has been described. With thepower supply apparatus of the present invention, in each of the powerrunning mode and the regenerative mode of the motor generators, electricpower balance is controlled to avoid generation of overcurrent ofconverter 110. As described below, the control of electric power balancecan be implemented as operation for control that is programmed inadvance in control unit (ECU) 15.

FIG. 5 is a flowchart illustrating the electric power balance control bythe control unit in the power running mode.

Referring to FIG. 5, in the power running mode, in response to operationof the accelerator by a driver for example, required torque Trq of motorgenerators MG1, MG2 is calculated (step S100). As shown in FIG. 3,according to the calculated required torque Trq and motor revolutionnumber N, optimum motor operating voltage Vm# is determined.

Motor operating voltage Vm is controlled independently of the processshown in the flowchart of FIG. 5 and the control is implemented byswitching control of converter 110 according to voltage command valueVmr corresponding to optimum motor operating voltage Vm# in FIG. 3. Inother words, voltage command value Vmr is determined according to motoroperating conditions and independently of torque command value Tref.

In response to the control of motor operating voltage Vm, an amount ofchange in capacitor power Pc, which is an amount of change in storedelectric power (P=C·V²/2) of smoothing capacitor 120 is calculated foreach control period (step S110).

This amount of change in capacitor power Pc is represented, using motoroperating voltage Vm applied to smoothing capacitor 120 and acapacitance value C of smoothing capacitor 120, as an amount of changein P=C·V²/2 in a control period T by expression (1). $\begin{matrix}\begin{matrix}{{Pc} = {\left\{ {{\frac{1}{2}{C \cdot \left( {{Vm} + {\Delta\quad{Vm}}} \right)^{2}}} - {\frac{1}{2}{C \cdot {Vm}^{2}}}} \right\} \cdot \frac{1}{T}}} \\{= {\frac{C}{2T}\left( {{{2 \cdot {Vm} \cdot \Delta}\quad{Vm}} + {\Delta\quad{Vm}^{2}}} \right)}}\end{matrix} & (1)\end{matrix}$

In expression (1), Vm represents a motor operating voltage in therelevant control period and ΔVm represents the difference in motoroperating voltage Vm between the control period and the immediatelypreceding control period. For example, in the i-th control period (i isnatural number), the difference is represented by the equation ΔVm(i)=Vm(i)−Vm (i−1). Thus, when motor operating voltage Vm increases, theamount of change in capacitor power Pc is larger than zero (Pc>0).

For example, an output value of a voltage sensor that detects the motoroperating voltage can be used as Vm in expression (1) to accuratelycalculate the amount of change in capacitor power Pc. Alternatively,voltage command value Vmr may be used as Vm in expression (1) forcalculating the amount of change in capacitor power Pc in order toreduce the load of calculation.

Further, motor consumption power Pm corresponding to required torque Trqis calculated. Then, a determination about electric power balance ismade, namely it is determined whether the sum of motor power Pm and theamount of change in capacitor power Pc determined in step S110 exceeds alimiting value of output electric power of the converter (hereinafterreferred to as converter output power limiting value) Pcvlm (step S120).

Converter output power limiting value Pcvlm is restricted for example bythe capacity of the power source, namely battery 10, and the electricpower (current) capacity of switching elements Q1, Q2 constitutingconverter 110. In particular, when converter output power limiting valuePcvlm is restricted, not by the capacity of battery 10 but by thecapacity of switching elements Q1, Q2, overcurrent could pass throughswitching elements Q1, Q2, which is a problem in terms of deviceprotection.

Accordingly, by determining whether or not the condition defined by thefollowing expression (2) is satisfied, it is determined whether or notmotor power Pm does not exceed a value calculated by subtracting theamount of change in capacitor power Pc (>0) from converter output powerlimiting value Pcvlm (step S130).Pm≦Pcvlm−Pc (in the power running mode, Pm, Pcvlm, Pc>0)  (2)

When the condition Pm≦Pcvlm−Pc is satisfied and electric power isconsumed by motor generator MG1, MG2 exactly as defined by requiredtorque Trq, it never occurs that motor power Pm exceeds converter outputpower limiting value Pcvlm. Then, torque command value Tref is set equalto required torque Trq (step S140).

On the contrary, when the condition Pm>Pcvlm−Pc is satisfied and motorgenerator MG1, MG2 consume electric power exactly as defined by requiredtorque Trq, the sum of motor power Pm and the amount of change incapacitor power Pc exceeds converter output power limiting value Pcvlm.In this case, motor power Pm is limited so that motor power Pm does notexceed converter output power limiting value Pcvlm, particularly so thatovercurrent is not generated in converter 110.

More specifically, a limiting value of the motor power, Pm#, whichsatisfies the condition represented by the expression Pm#=Pcvlm−Pc iscalculated, and torque command value Tref is calculated according tothis motor power Pm#. In other words, torque command value Tref islimited to be smaller than original required torque Trq (step S150).

In accordance with torque command value Tref determined and calculatedin step S140 or S150, inverters 131, 132 are switching-controlled andthe torque (i.e., motor current) of motor generators MG1, MG2 iscontrolled (step S160).

With the above-described control and the structure that allows the inputvoltage (motor operating voltage Vm) to the motor drive control unit(inverter) to be varied by the converter, the motor control and theconverter control are performed in coordination with each other so thatthe output power supplied from the converter can be prevented frombecoming excessive. In other words, the output electric power ofconverter 110 does not exceed its limiting value Pcvlm and thusovercurrent of converter 110 can be prevented to achieve deviceprotection.

When a plurality of loads, namely motors (motor generators) are providedas this embodiment, the sum of consumption power of the motors may becalculated as motor power Pm.

Electric power balance control in the regenerative mode is nowdescribed. As discussed above, when the converter operates to increasethe voltage, motor operating voltage Vm is increased according to motoroperating conditions and the motor power of motor generators (MG1, MG2)in the power running mode is limited as required.

In contrast, when the motor generators operate in the regenerative mode,optimum motor operating voltage Vm# decreases according to motoroperating conditions. Then, regarding the electric power balance controlin the regenerative mode, braking ability deteriorates if theregenerative power of the motor generators is limited. Therefore, ifcontrol in the regenerative mode is performed in similar manner to thatapplied in the process of increasing the voltage, there could ariseproblems in terms of safety and driver's physical feelings. Accordingly,in the regenerative mode, the electric power balance control is carriedout in the manner as described below.

FIG. 6 is a flowchart illustrating the electric power balance control inthe regenerative mode.

Referring to FIG. 6, as the electric power balance control in theregenerative mode is started, control unit 15 calculates motorregenerative power Pm (<0) (step S200). As in step S120, when aplurality of motors (motor generators) that generate electric power areprovided, the sum of regenerative power of these motors is calculated asmotor power Pm.

Further, as in step S110 shown in FIG. 5, the amount of change incapacitor power Pc is calculated based on expression (1) (step S210).

Then, the balance between motor regenerative power Pm (<0) and amount ofchange in capacitor power Pc (<0) that are calculated in respectivesteps S200, S210 and a limiting value of electric power input to theconverter (hereinafter “converter input power limiting value”) Pcvlm(<0) is determined. Specifically, it is determined whether or notexpression (4) that is a modified version of expression (3) with thepolarity in expression (2) inverted is satisfied (step S220).Pm>Pcvlm−Pc (in the regenerative mode, Pm, Pcvlm, Pc<0)  (3)Pc≧Pcvlm−Pm  (4)

Under the condition that expression (4) is satisfied, even if motoroperating voltage Vm is varied as shown in FIG. 3 according to motoroperating conditions, it never occurs that input electric power toconverter 110 becomes excessive. Thus, voltage command value Vmr ofmotor operating voltage Vm is set to optimum motor operating voltage Vm#that is calculated based on FIG. 3 (step S230).

When expression (4) is not satisfied, it is further determined whetheror not motor regenerative power Pm exceeds converter input powerlimiting value Pcvlm (step S240).

When the condition Pm<Pcvlm is satisfied, namely the absolute value ofmotor regenerative power Pm is larger than the absolute value ofconverter input power limiting value Pcvlm, voltage command value Vmr isfixed to the same value as the one in the immediately preceding controlperiod in order to inhibit decrease of motor operating voltage Vm thatis done according to motor operating conditions (step S250).

In this case, while motor operating voltage Vm deviates from the optimumvalue in accordance with operating conditions and consequently powerconsumption of inverters 131, 132 increases, the regenerative power ofthe motor generators is not restricted and thus the braking ability doesnot deteriorate.

On the contrary, when the condition Pm≧Pcvlm is satisfied, namely theabsolute value of motor regenerative power Pm is equal to or smallerthan the absolute value of converter input power limiting value Pcvlm,motor operating voltage Vm cannot be decreased to optimum voltage Vm#precisely in accordance with motor operating conditions. However, motoroperating voltage Vm is allowed to be decreased within the range inwhich the difference determined by Pcvlm−Pm is equal to the amount ofchange in capacitor power Pc. In other words, the amount of change inmotor operating voltage (ΔVm) is determined within the range in whichthe following expression (5) is satisfied. $\begin{matrix}{{\frac{1}{T}\left\{ {{\frac{C}{2}\left( {{Vm} + {\Delta\quad{Vm}}} \right)^{2}} - {\frac{C}{2} \cdot {Vm}^{2}}} \right\}} = {{Pcvlm} - {Pm}}} & (5)\end{matrix}$

The left side of expression (5) corresponds to the amount of change incapacitor power Pc as the motor operating voltage is changed from Vm toVm+ΔVm in a control period T. Namely, Vm represents motor operatingvoltage Vm in the immediately preceding control period.

ΔVm in expression (5) is determined as shown by the following expression(6). $\begin{matrix}{{\Delta\quad{Vm}} = {{- {Vm}} + \sqrt{{- {Vm}^{2}} + \frac{2 \cdot T \cdot \left( {{Pcvlm} - {Pm}} \right)}{C}}}} & (6)\end{matrix}$

Voltage command value Vmr of the motor operating voltage is allowed todecrease while the amount of change ΔVm is limited based on expression(6) (step S260). In this way, based on the difference between motorregenerative power Pm and converter input power limiting value Pcvlm,the amount of decrease in voltage command value is limited so that motoroperating voltage Vm is decreased in the range that does not exceedsconverter input power limiting value Pcvlm so as to improve efficiencyof motor generators MG1, MG2.

Thus, based on voltage command value Vmr that is determined in one ofsteps S230, S250 and S260, switching control of the converter isperformed to control motor operating voltage Vm (step S270).

Accordingly, when motor generators MG1, MG2 operate in the regenerativemode, the control can be implemented without limiting regenerative powerof motor generators MG2, MG2, in such a manner that allows electricpower input to converter 110 not to exceed its limiting value Pcvlm inconsideration of the amount of change in capacitor power. Overcurrent ofconverter 110 can thus be avoided and accordingly device protection isachieved.

While this embodiment includes the structure as illustrated above withwhich two AC electric motors are driven and controlled by the powersupply apparatus, the present invention is applicable to a power supplyapparatus and a motor drive control method for driving and controllingnot only AC electric motors but also DC electric motors under thecondition that the torque (electric power) of the motors can becontrolled by the motor drive control unit (corresponding to theinverter in the present embodiment).

Further, the number of motors driven and controlled by the power supplyapparatus is not limited to a particular number, and the presentinvention is applicable to a power supply apparatus driving andcontrolling an arbitrary number of motors. In this case, a power supplyapparatus controlling and driving a plurality of motors may calculatethe consumption power and regenerative power of the motors as shown inFIGS. 5 and 6 as the sum of consumption power and regenerative power ofthese motors.

Moreover, the power supply apparatus of the present invention isapplicable to such vehicles as electric vehicles in addition to hybridelectric vehicles and further applicable to various equipment andsystems having a motor to be driven and controlled.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

INDUSTRIAL APPLICABILITY

The power supply apparatus as well as the motor drive control method ofthe present invention are applicable to equipment and systems havingmotor(s) mounted thereon and driven and controlled by a power supplyapparatus, the equipment and systems including such vehicles havingmotor(s) mounted thereon as hybrid electric vehicles and electricvehicles.

1. A power supply apparatus driving and controlling a motor, comprising:a DC power supply; a converter converting a first DC voltage from saidDC power supply into a second DC voltage according to a voltage commandvalue to output said second DC voltage between a first power supply lineand a second power supply line; a chargeable and dischargeable electriccharge storage unit connected between said first power supply line andsaid second power supply line; a motor drive control unit receiving saidsecond DC voltage between said first power supply line and said secondpower supply line and converting, according to a driving force commandvalue, said second DC voltage into electric power for driving andcontrolling said motor; and a control unit adjusting, when said motoroperates in a power running mode, said driving force command value toallow the sum of electric power consumed by said motor according to saiddriving force command value and an amount of change in stored electricpower of said electric charge storage unit, said change being caused assaid second DC voltage changes, to be smaller than a limiting value ofelectric power output from said converter.
 2. The power supply apparatusaccording to claim 1, wherein said voltage command value is determinedaccording to the number of revolutions and a required driving force ofsaid motor and independently of said driving force command value.
 3. Thepower supply apparatus according to claim 1, wherein said DC powersupply is chargeable, said motor drive control unit converts, when saidmotor operates in a regenerative mode, the electric power generated bysaid motor into said second DC voltage according to said voltage commandvalue and outputs said second DC voltage between said first power supplyline and said second power supply line, said converter converts, whensaid motor operates in said regenerative mode, said second DC voltageinto said first DC voltage to charge said DC power supply, and saidcontrol unit adjusts, when said motor operates in said regenerativemode, said voltage command value as required based on a relation betweena combination of the electric power generated by said motor and anamount of change in stored electric power of said electric chargestorage unit that is caused by a change of said second DC voltage and alimiting value of electric power input to said converter.
 4. The powersupply apparatus according to claim 3, wherein when said motor operatesin said regenerative mode, said voltage command value is adjusted bysaid control unit as required, after temporarily determined according tothe number of revolutions and a required driving force of said motor. 5.The power supply apparatus according to claim 3, wherein said controlunit inhibits, when said motor operates in said regenerative mode andthe electric power generated by said motor exceeds the limiting value ofelectric power input to said converter, decrease of said voltage commandvalue.
 6. he power supply apparatus according to claim 3, wherein saidcontrol unit restricts, when said motor operates in said regenerativemode and the electric power generated by said motor is smaller than thelimiting value of electric power input to said converter, an amount ofdecrease in said voltage command value so as to balance the amount ofchange in stored electric power of said electric charge storage unitthat is caused by the change of said second DC voltage with acombination of the limiting value of electric power input to saidconverter and the electric power generated by said motor.
 7. The powersupply apparatus according to claim 1, wherein said control unitcalculates said amount of change in stored electric power based on saidvoltage command value.
 8. The power supply apparatus according to claim1, wherein said control unit calculates said amount of change in storedelectric power based on a detected value of said second DC voltage.
 9. Amotor vehicle comprising: a power supply apparatus as recited in claim1; and an AC electric motor provided as said motor driven and controlledby said power supply apparatus and capable of driving at least onewheel, said converter provided as a voltage step-up converter capable ofmaking said second DC voltage higher than said first DC voltage, andsaid motor drive control unit including an inverter making conversionbetween said second DC voltage and an AC voltage for driving andcontrolling said AC electric motor.
 10. A motor drive and control methodfor driving and controlling a motor by a power supply apparatus, saidpower supply apparatus including: a DC power supply; a converterconverting a first DC voltage from said DC power supply into a second DCvoltage according to a voltage command value to output said second DCvoltage between a first power supply line and a second power supplyline; a chargeable and dischargeable electric charge storage unitconnected between said first power supply line and said second powersupply line; and a motor drive control unit converting, according to adriving force command value, said second DC voltage between said firstpower supply line and said second power supply line into electric powerfor driving and controlling said motor, said method comprising a firststep of adjusting, when said motor operates in a power running mode,said driving force command value to allow the sum of electric powerconsumed by said motor according to said driving force command value andan amount of change in stored electric power of said electric chargestorage unit, said change being caused as said second DC voltagechanges, to be smaller than a limiting value of electric power outputfrom said converter.
 11. The motor drive and control method according toclaim 10, wherein said voltage command value is determined according tothe number of revolutions and a required driving force of said motor andindependently of said driving force command value.
 12. The motor driveand control method according to claim 10, wherein said DC power supplyis chargeable, said motor drive control unit converts, when said motoroperates in a regenerative mode, the electric power generated by saidmotor into said second DC voltage according to said voltage commandvalue and outputs said second DC voltage between said first power supplyline and said second power supply line, said converter converts, whensaid motor operates in said regenerative mode, said second DC voltageinto said first DC voltage to charge said DC power supply, and saidmotor drive control method further comprises a second step of adjusting,when said motor operates in said the regenerative mode, said voltagecommand value as required based on a relation between a combination ofthe electric power generated by said motor and an amount of change instored electric power of said electric charge storage unit that iscaused by a change of said second DC voltage and a limiting value ofelectric power input to said converter.
 13. The motor drive and controlmethod according to claim 12, wherein when said motor operates in saidregenerative mode, said voltage command value is temporarily determined,before said second step is carried out, according to the number ofrevolutions and a required driving force of said motor.
 14. The motordrive and control method according to claim 12, wherein said second stepincludes a sub step of inhibiting, when said motor operates in saidregenerative mode and the electric power generated by said motor exceedsthe limiting value of electric power input to said converter, decreaseof said voltage command value.
 15. The motor drive and control methodaccording to claim 12, wherein said second step includes a sub step ofrestricting, when said motor operates in said regenerative mode and theelectric power generated by said motor is smaller than the limitingvalue of electric power input to said converter, an amount of decreasein said voltage command value so as to balance the amount of change instored electric power of said electric charge storage unit that iscaused by the change of said second DC voltage with a combination of thelimiting value of electric power input to said converters and theelectric power generated by said motor.
 16. The motor drive and controlmethod according to claim 10, wherein in said first or second step, saidamount of change in stored electric power is calculated based on saidvoltage command value.
 17. Te motor drive and control method accordingto claim 10, wherein in said first or second step, said amount of changein stored electric power is calculated based on a detected value of saidsecond DC voltage.